Shifty student that's sore over bet being exposed (6)
I believe the answer is:
louche
'shifty' is the definition.
(I've seen this before)
'student that's sore over bet being exposed' is the wordplay.
'student' becomes 'L' (as in L-plates for learner drivers).
'that's sore' becomes 'ouch' (expression of pain).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'being exposed' means to look at the middle letters (outside letters removed).
The middle of 'bet' is 'e'.
'l'+'ouch'+'e'='LOUCHE'
(Other definitions for louche that I've seen before include "Seedy" , "Ignominious" , "Appealingly sordid" , "Appealingly disreputable" , "Rakishly disreputable" .)